1. Field of the Invention
The present invention relates to optical systems including an optical connector, laser apparatus, etc.
2. Description of the Related Art
Recently, there has been a trend toward integration of lasers with other optical parts. In some cases, a laser beam emitted from a laser and advancing in a direction parallel to a substrate must be coupled to a light beam which advances at right angles or a specific angle to the substrate.
Conventionally, this is attained by guiding the output laser beam from the laser to a straight waveguide, and coupling it to a light beam radiated to the outside of the substrate, by means of a grating arranged on the upper surface of the waveguide.
In an optical connector designed for this purpose, the light beam is exponentially attenuated as it passes under the grating. If the coupling efficiency is increased so that a greater volume of light can be taken out, therefore, the light beam radiated from the grating enjoys an intensity distribution such that it becomes more intense with distance from the emission side. The light beam with such an intensity distribution is not desirable for use. Generally, moreover, the grating is too long. If the light beam to be radiated from the grating has a uniform intensity, on the other hand, the coupling efficiency is considerably lowered.
The light beams which can be taken out by means of the optical connector of this type are limited to straight polarized light. This imposes restrictions on optical design, and many optical systems utilize circular polarized light.
Accordingly, there is a demand for compact optical elements which can efficiently couple radiant light beams having a uniform intensity distribution and a high degree of freedom for polarized light. In many cases, moreover, a laser having a Fabry-Perot resonator should be provided with a resonator end mirror in a substrate, which constitutes a substantial hindrance to integration. In order to cope with this, the so-called ring laser apparatus is under investigation in which a ring-shaped waveguide is used as the resonator. Since light continues to circulate through the waveguide in the ring laser apparatus, there is no need of a reflective end face which is essential to the Fabry-Perot resonator. The ring laser apparatus is provided with a waveguide which is connected to or extends beside the ring-shaped waveguide, whereby light is taken out from the waveguide. A light beam introduced into the waveguide is taken out by means of the optical connector which has the grating on its surface, as mentioned before.
In the case of this system, there is the problem of an optical loss at the junction between the ring and straight portion, as well as the aforesaid problem of the optical connector itself. Further, the system occupies an increased volume in the whole apparatus. Under these circumstances, there is a demand for a more immediate method for taking out light from the ring laser apparatus having the ring-shaped waveguide to the outside of the substrate.